University of Central Florida STARS Electronic Theses and Dissertations, 2004-2019 2018 Brain Stethoscope: A Non-invasive Method for Monitoring Intracranial Pressure Md Khurshidul Azad University of Central Florida Part of the Electro-Mechanical Systems Commons Find similar works at: https://stars.library.ucf.edu/etd University of Central Florida Libraries http://library.ucf.edu This Masters Thesis (Open Access) is brought to you for free and open access by STARS. It has been accepted for inclusion in Electronic Theses and Dissertations, 2004-2019 by an authorized administrator of STARS. For more information, please contact [email protected]. STARS Citation Azad, Md Khurshidul, "Brain Stethoscope: A Non-invasive Method for Monitoring Intracranial Pressure" (2018). Electronic Theses and Dissertations, 2004-2019. 5824. https://stars.library.ucf.edu/etd/5824 BRAIN STETHOSCOPE: A NON-INVASIVE METHOD FOR MONITORING INTRACRANIAL PRESSURE By MD KHURSHIDUL AZAD B.S RAJSHAHI UNIVERSITY OF ENGINEERING & TECHNOLOGY, BANGLADESH 2009 A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in the Department of Mechanical and Aerospace Engineering in the College of Engineering and Computer Science at the University of Central Florida Orlando, Florida Spring Term 2018 Major Professor: Hansen A. Mansy © 2018 Md Khurshidul Azad ii ABSTRACT Monitoring intracranial pressure (ICP) is important for patients with increased intracranial pressure. Invasive methods of ICP monitoring include lumbar puncture manometry, which requires high precision, is costly, and can lead to complications. Non-invasive monitoring of ICP using tympanic membrane pulse (TMp) measurement can provide an alternative monitoring method that avoids such complications. In the current study, a piezo based sensor was designed, constructed and used to acquire TMp signals. The results showed that tympanic membrane waveform changed in morphology and amplitude with increased ICP, which was induced by changing subject position using a tilt table. In addition, the results suggest that TMp are affected by breathing, which has small effects on ICP. The newly developed piezo based brain stethoscope may be a way to monitor patients with increased intracranial pressure thus avoiding invasive ICP monitoring and reducing associated risk and cost. iii ACKNOWLEDGMENTS I am extremely grateful to Dr. Hansen Mansy, my thesis advisor, who has continuously inspired and mentored me to achieve my research goals. He helped me understand the motivation of the research and supported me with his ideas and guidance throughout this research. I would like to thank Dr. Kassab and Dr. Bhattacharya for their valuable inputs. In addition, I would like to thank Andrew Spiewak as well as my other colleagues in Biomedical Acoustic Research Laboratory for their continuous support. iv TABLE OF CONTENTS LIST OF FIGURES ..................................................................................................................... viii CHAPTER 1 : INTRODUCTION .................................................................................................. 1 1.1 Cerebrospinal Fluid and Intracranial Pressure ................................................................. 2 1.2 Inner Ear ........................................................................................................................... 4 1.3 Relation Between CSF Pressure and Cochlear Fluid Pressure ........................................ 6 1.4 Middle Ear ........................................................................................................................ 6 1.5 Tympanic Membrane and External Ear ........................................................................... 7 1.6 Variation of CSF Pressure and ICP with Respect to Body Posture ................................. 8 1.7 Effect of Tympanic Membrane Movement on Intracranial Pressure ............................. 10 1.8 Measurement of Tympanic Membrane movement using volume displacement ........... 11 1.9 Relation between CSF Flow and Cerebral Blood Flow ................................................. 14 CHAPTER 2 : METHODS ........................................................................................................... 17 2.1 Building the Sensor Assembly ....................................................................................... 17 2.2 Data acquisition, Post Processing and Analyzing the Acquired TMp Data ................... 18 2.2.1 Data Acquisition, Plotting the Acquired Tympanic Membrane Waveform with Earlobe Pulse and Airflow .................................................................................................... 18 2.2.2 Filtering the acquired signals .................................................................................. 19 2.2.3 Identifying the Peaks of Ear lobe pulse .................................................................. 20 v 2.2.4 Finding the Nadirs (start and end points) of Individual TMp waveforms .............. 21 2.2.5 Separating the Individual TMp Events ................................................................... 22 2.2.6 Average TMp Waveform and Normalized Deviation from Mean .......................... 23 2.2.7 Effect of Breathing on Tympanic Membrane Pulsations ........................................ 25 2.2.8 Separating the TMp Events Based on Lung Volume .............................................. 26 2.2.9 Mean TMp for High and Low Lung Volume ......................................................... 29 2.3 Testing the TMp Sensor Output Using Mechanical Setup ............................................. 30 2.3.1 Experimental Setup ................................................................................................. 30 2.3.2 Testing the sensor output with multiple input signals ............................................ 32 2.3.3 Testing Repeatability of the Piezo based TMp Sensor Output ............................... 35 2.3.4 Testing the Repeatability of LASER Doppler Vibrometer Output ......................... 36 2.3.5 Testing the Effect of External Pressure on TMp Sensor Output ............................ 37 2.4 Testing the Effect of Dead Space in the System on TMp Signal Output ....................... 38 2.5 Testing the effect of leakage on TMp Signals................................................................ 41 2.6 Testing the repeatability of the TMp signal ................................................................... 44 2.7 Investigating the difference between contralateral ears ................................................. 45 2.8 Testing the Effect of External Pressures on TMp Signals ............................................. 46 CHAPTER 3 : TYMPANIC MEMBRANE PULSATIONS AT VARYING TILT ANGLE ...... 48 3.1 Experimental Procedure ................................................................................................. 48 vi 3.2 Results ............................................................................................................................ 49 3.3 TMp changes with title angle for shorter acquisition and settling times ....................... 56 CHAPTER 4 : SIMPLIFIED MODEL OF TYMPANIC MEMBRANE PULSATIONS ........... 62 4.1 Model Geometry ............................................................................................................ 62 4.2 Results ............................................................................................................................ 64 CHAPTER 5 : DISCUSSION AND CONCLUSION .................................................................. 67 5.1 Discussion ...................................................................................................................... 67 5.1.1 Other Approaches of TMp Measurement ............................................................... 67 5.1.2 Repeatability of the Piezo Sensor Output ............................................................... 70 5.1.3 Repeatability of TMp signals in Human Subjects .................................................. 71 5.1.4 Effect of Body Posture on TMp .............................................................................. 71 5.1.5 Simplified Numerical Model .................................................................................. 72 5.2 Future Work ................................................................................................................... 73 5.3 Conclusion ...................................................................................................................... 74 LIST OF REFERENCES .............................................................................................................. 75 vii LIST OF FIGURES Figure 1-1CSF System Showing the CSF fluid in cranial subarachnoid space as well as ventricular places. [2] ........................................................................................................................................ 2 Figure 1-2 ICP waveform acquired by inserting ICP sensor through subdural cavity. (a) the whole duration of the signal (b) zoomed in version of 6 second time window. [5] .................................. 3 Figure 1-3 Inner ear showing Cochlea and the vestibular system. The inner ear is filled with Perilymph and Endolymph. Both fluid is connected to CSF through cochlear aqueduct and endolymphatic sac respectively. [6] ................................................................................................ 4 Figure 1-4(a): Cross